Velocity of a Neutrino

[swansont]

 

I'm not sure what you are trying to say, here. However, there is thought to be a "cosmic neutrino background" equivalent of the cosmic microwave background (CMB). This would consist of neutrinos released 380,000 years before the CMB and hence would be at an even lower temperature. If we were able to detect these low energy neutrinos, they would give us a lot of information about the early universe. But it seems unlikely they can ever be detected.

 

However, at 3K a particle (assuming these neutrinos could be thermalized) has a kinetic energy (kT) of a few 10-4 eV. If the rest mass is ~1 eV, this means v/c is around 0.01

 

That's nowhere near being at rest with respect to us. It also points out that a neutrino taking just that tiny amount of energy away from an interaction is moving quite fast.

[DimaMazin]

 

 

 

Any large-scale effect, e.g. expansion, would happen for the neutrinos as well as us. Aside from that, how would you accelerate a neutrino?

Do you think acceleration of universe expansion doesn't reduce speed of neutrino?

[Strange]

Do you think acceleration of universe expansion doesn't reduce speed of neutrino?

 

It is nothing to do with accelerating expansion; it is just the expansion.

[ACG52]

The Opera measurements, the correct ones, cannot detect any difference between the speed of the neutrino and light.

[Strange]

The Opera measurements, the correct ones, cannot detect any difference between the speed of the neutrino and light.

 

Indeed. I would like to thank aViolentBee for asking the question; it prompted me to go and find out what the final results were!

[DimaMazin]

 

It is nothing to do with accelerating expansion; it is just the expansion.

What about this?http://en.wikipedia.org/wiki/Accelerating_universe

[Strange]

What about this?http://en.wikipedia.org/wiki/Accelerating_universe

 

What about it?

[MigL]

Well if the neutrino is coming from another galaxy cluster which is receding from our local group, then, as it travels at a speed close to c, the separation between its origin and destination increases. Its effective speed is therefore reduced and it loses energy.

Even if the neutrino was massless, it would still lose energy as the separation increased, but it would manifest as redshift instead.

 

I would agree with Dima.

But the fact remains that we would not detect low energy neutrinos.

As Strange has said, the neutrino background radiation would provide even more information about the big bang than the CMB as it is much closer to t=0.

[DimaMazin]

 

What about it?

I have mistaken there.We already see redshift due to increased speeds of galaxies. If galaxies speeds will infinitely increase then they will reduce energy of radiated neutrinos. Therefore at defined moment we can have neutrinos with zero speed, then our gravitation will grasp the neutrinos and turn them into dark matter.Using an electromagnet and measurement of mass, before and after division, we can detect them.

[Strange]

Two problems with that. Firstly, there is a "horizon" which limits the lowest energy of neutrinos we see.

 

 

Using an electromagnet and measurement of mass, before and after division, we can detect them.

 

You can't detect neutrinos with an electromagnet (the clue is in the name: little neutral ones). They can only be detected because highly energetic neutrinos have a minute chance of being caught by a nucleus. Out of the billions of neutrinos that flood through a detector, only a small number are detected.

[DimaMazin]

Two problems with that. Firstly, there is a "horizon" which limits the lowest energy of neutrinos we see.

 

 

You can't detect neutrinos with an electromagnet (the clue is in the name: little neutral ones). They can only be detected because highly energetic neutrinos have a minute chance of being caught by a nucleus. Out of the billions of neutrinos that flood through a detector, only a small number are detected.

We can detect dark matter.When neutrinos increase dark matter by own amount we can detect increasing of dark matter. Also we can define expecting quantity of neutrinos which will be grasped by the gravitation due to reducing of their speed.Only a great number can be detected.

[Strange]

And there is no reason to think that there are enough low-energy (cold) neutrinos to make a significant contribution to dark matter. (Neutrinos were an obvious candidate, but they have fairly definitely been eliminated. Apart from the hypothetical "sterile neutrino" - which is even harder to detect!)

[DimaMazin]

Neutrinos were an obvious candidate, but they have fairly definitely been eliminated.

Now that's correct,but I say about future.

[swansont]

Do you think acceleration of universe expansion doesn't reduce speed of neutrino?

 

Did you read the post to which you responded? I said expansion will affect the neutrinos. I also gave a calculation about neutrinos that had an energy of the CMB.

 

How about you calculate how much KE a neutrino has if it's moving at some locally relevant speed, say, of order 100 km/s, and has a mass of 1eV.

[DimaMazin]

 

Did you read the post to which you responded? I said expansion will affect the neutrinos. I also gave a calculation about neutrinos that had an energy of the CMB.

 

How about you calculate how much KE a neutrino has if it's moving at some locally relevant speed, say, of order 100 km/s, and has a mass of 1eV.

1eV/c²=1.782662_*10^-36kg

1eV is energy. What did you mean "a mass of 1eV "?

[swansont]

1eV/c²=1.782662_*10^-36kg

1eV is energy. What did you mean "a mass of 1eV "?

 

Mass is often represented as an energy. Division by c² is implied; for rest mass, m = E/c² as you have done.

[DimaMazin]

 

Did you read the post to which you responded? I said expansion will affect the neutrinos. I also gave a calculation about neutrinos that had an energy of the CMB.

 

How about you calculate how much KE a neutrino has if it's moving at some locally relevant speed, say, of order 100 km/s, and has a mass of 1eV.

gamma -1=5.56_*10^-8

KE=5.56_*10^-8_*1.78_*10^-36_*9_*10¹⁶_*6.24_*10¹⁸=5.56_*10^-8eV

I think I have complicated.

[andrewcellini]

1eV/c²=1.782662_*10^-36kg

1eV is energy. What did you mean "a mass of 1eV "?

yes 1 eV is energy however, 1 eV/c^2 is a unit of mass derived from mass energy equivalence.

[DimaMazin]

yes 1 eV is energy

In this case I call that by gravitational energy.

KE=(gamma - 1) _* gravitational energy(eV units)

[elfmotat]

In this case I call that by gravitational energy.

KE=(gamma - 1) _* gravitational energy(eV units)

 

No, don't do that. That makes no sense.

[andrewcellini]

In this case I call that by gravitational energy.

KE=(gamma - 1) _* gravitational energy(eV units)

Why? How did you derive this?

[DimaMazin]

 

No, don't do that. That makes no sense.

Yes. We should turn the appeared Joules into eVolts:

KE=(gamma - 1) _* gravitational energy(eV units) _* 6.24150934_*10¹⁸

[elfmotat]

Yes. We should turn the appeared Joules into eVolts:

KE=(gamma - 1) _* gravitational energy(eV units) _* 6.24150934_*10¹⁸

 

No, you're making up nonsense. Kinetic energy and gravitational energy are not the same, and gravitational energy has absolutely nothing to do with the gamma factor in special relativity. Equations don't make sense just because they're dimensionally consistent.

[DimaMazin]

 

No, you're making up nonsense. Kinetic energy and gravitational energy are not the same, and gravitational energy has absolutely nothing to do with the gamma factor in special relativity. Equations don't make sense just because they're dimensionally consistent.

Then what is equation of neutrino KE?

[Strange]

Then what is equation of neutrino KE?

 

Same as anything else:

[math]\displaystyle m_o c^2 \left(\frac{1}{\sqrt{1-\frac{v^2}{c^2}}} - 1 \right)[/math]